(CNN) -- A day after six Baltimore police officers pleaded not guilty to all charges in Freddie Gray's death, a newspaper reported his autopsy shows he suffered a "high-energy injury" most likely caused by a sudden slowing of the police van holding him.

The injury was likened to a shallow-water diving accident, according to the Baltimore Sun's account of a copy of the autopsy report.

The state medical examiner's office declared Gray's death a homicide because officers failed to follow safety guidelines "through acts of omission," according to a copy of the report obtained by the newspaper.

The report provides a better picture of what happened to Gray, whom police put on his belly in the back of the van. Gray wasn't belted down, and he may have rose to his feet and then was slammed against an interior panel during an abrupt change in direction, according to the newspaper's account of the autopsy report.

With his ankles and wrists shackled, Gray was "at risk for an unsupported fall during acceleration or deceleration of the van," according to the newspaper's summary of the report.

Gray tested positive for opiates and cannabinoid, according to the newspaper's account of the autopsy.

The autopsy report has yet to be made public.

The six officers and their attorneys haven't seen a copy of the report, the attorneys said in a joint statement Tuesday.

"It was our understanding that the only copy of the autopsy was in the possession of the State's Attorney's Office and the State Medical Examiner's Officer," the defense attorneys said in a statement. "We were expecting, and continue to expect, all discovery, including the autopsy, to be turned over to us by no later than Friday, June 26."

The Office of the Chief Medical Examiner in Baltimore isn't releasing the autopsy report because it's evidence in a criminal case, spokesman Bruce Goldfarb said.

The prosecutor's office also declined to release a copy of the report.

The six officers pleaded not guilty Monday to all charges against them, court records said. They face charges that, if they are convicted, could lead to decades in prison, based on their alleged actions in Gray's death. Among them: illegal arrest, misconduct, assault and involuntary manslaughter.

Gray, 25, was arrested on a weapons charge April 12 but suffered a severe spinal cord injury while in police custody that led to his death seven days later. His death sparked protests and riots in Baltimore.

Pleading not guilty were Officer Garrett E. Miller, who joined the force in 2012; Lt. Brian W. Rice, an officer since 1997; Officer Edward M. Nero, on the job since 2012; Officer Caesar R. Goodson Jr., a veteran since 1999; Sgt. Alicia D. White, on the force since 2010; and Officer William G. Porter, who joined the force in 2012.

Goodson, who prosecutors say was driving the van used to transport Gray after his arrest, faces the most charges, and the most severe: second-degree depraved-heart murder.